This is a timely thread. On Thursday, I went to my coin dealer and we discussed this very topic. I am extremely lucky, my coin dealer is incredibly reputable and honest.
He saves up until he has about 100 coins, silver and gold, to submit at one time. He showed me a few of them, and then I asked him the following question:
"What do you think they'll grade?"
His reply:
"I have some 4's, 5's, and maybe a few 6's. (MS 64, 65, 66)." I asked 'What about higher than that?" He said "Maybe, once in a while you hit one like that."
Grading is largely, key word 'largely,' an objective standard. However, there is an artistic component to grading. You really see where that comes in when you start talking about the difference between a MS 65-66, and grades higher. Certain coins - for no objective reason you can articulate - just strike you as better than others. Maybe it's the way they catch the light, maybe certain features are so razor sharp, or the way the fields are are certain character of smoothness. When you get to grades MS-65 and above, there may be no real discernible difference between a 66 and a 67, or there might be. Again, it's a bit of an art at that point.
While it is good advice to say 'buy the coin, not the holder' - and one I ascribe to, the fact is that number makes a major difference financially. So there will be an incentive to have 'perfect' coins. The reality is a truly 'perfect' coin is extremely rare, whereas an MS-70 isn't nearly so rare. Hence, it is a bit of a stock market. Perception of a grade is just as important as the 'actual' grade at those levels. Since the resulting difference in one grade point can be thousands of dollars, you are necessarily taking a risk.
I do like the 'investment' component of collecting, however, ultimately, I buy what I like. I also do not become overly attached to a number grade. My current penny collection (59-2012) is all MS. Are there any 70's in there? Maybe, I don't know. But an inherent part of investing is risk. And that 'risk' is quantifiable as the art of grading when it comes to coins.
In general, I buy what I like, and don't worry about the number overly much - unless there's a huge price jump between grades, in which case, I go for the best looking coin in the lower grade.
Perfection is nice, but not realistic in the world we live in.